System and method of operation of an embedded system for a digital capacitance diaphragm gauge

ABSTRACT

Systems and methods for digitally controlling sensors. In one embodiment, a digital controller for a capacitance diaphragm gauge is embedded in a digital signal processor (DSP). The controller receives digitized input from a sensor AFE via a variable gain module, a zero offset module and an analog-to-digital converter. The controller automatically calibrates the received input by adjusting the variable gain and zero offset modules. The controller also monitors and adjusts a heater assembly to maintain an appropriate temperature at the sensor. The controller utilizes a kernel module that allocates processing resources to the various tasks of a gauge controller module. The kernel module repetitively executes iterations of a loop, wherein in each iteration, all of a set of high priority tasks are performed and one of a set of lower priority tasks are performed. The controller module thereby provides sensor measurement output at precisely periodic intervals, while performing ancillary functions as well.

RELATED APPLICATION

This application is a continuation of, and claims the benefit under 35U.S.C. §120 to, U.S. patent application Ser. No. 10/848,739, filed May19, 2004, entitled “SYSTEM AND METHOD OF OPERATION OF AN EMBEDDED SYSTEMFOR A DIGITAL CAPACITANCE DIAPHRAGM GAUGE,” now U.S. Pat. No. 7,010,938,which is a division of, and claims the benefit under 35 U.S.C. §120 to,U.S. patent application Ser. No. 10/063,991, filed May 31, 2002,entitled “SYSTEM AND METHOD OF OPERATION OF AN EMBEDDED SYSTEM FOR ADIGITAL CAPACITANCE DIAPHRAGM GAUGE,” now U.S. Pat. No. 6,910,381, eachof which is hereby incorporated herein by reference in its entirety.

BACKGROUND OF INVENTION

1. Technical Field of the Invention

This invention relates generally to the systems and methods foroperation of sensors and more particularly to embedded control systemsfor a digital capacitance diaphragm gauge using an advanced digitalsignal processor, including kernel and gauge control algorithms toprocess internal gauge functions.

2. Background of the Invention

Many manufacturing processes require accurate and repeatable pressuremeasurements during critical process steps. These processes may rely oncapacitance diaphragm gauges to achieve an accurate determination ofprocess chamber pressure. Capacitance diaphragm gauges (or capacitancemanometers) are widely used in the semiconductor industry. In part, thisis because they are typically well suited to the corrosive services ofthis industry. They are also favored because of their high accuracy andimmunity to contamination.

A capacitance manometer is a type of sensor which may be used to measureparameters such as the pressure within a process chamber. A capacitancemanometer has a housing containing two chambers separated by adiaphragm. One of the chambers is in fluid communication with theprocess chamber or conduit in which the pressure is to be measured.

The other chamber of the manometer is a typically (although notnecessarily) evacuated. It is a pressure reference chamber. Plates arelocated on the manometer housing and on the diaphragm. These plates havea capacitance that can be measured. When the process gas enters thefirst chamber, it exerts a pressure against the diaphragm and causes thediaphragm to move. The capacitive plate connected to the diaphragm isconsequently moved toward the plate connected to the manometer housing,changing the capacitance between the plates. The change in capacitancecorresponds to the increase in pressure and can be used as a measurementof the pressure.

Capacitance manometers typically operate by measuring the change inelectrical capacitance that results from the relative movement of thesensing electrodes. The change in capacitance can be measured usingvarious different types of electrical interfaces, such as balanced diodebridge interfaces, guarded secondary transformer-based bridgeinterfaces, and matched reference capacitor bridge interfaces. Theseinterfaces measure changes in capacitance, using circuitry coupled tothe capacitive plates of the manometer in order to determine changes intheir capacitance and corresponding changes in the measured parameter.

One of the major advantages of a capacitance diaphragm gauge is itsability to detect extremely small diaphragm movements, hence extremelysmall changes in the measured process parameter. The accuracy of thesesensors is typically 0.25 to 0.5% of the generated reading. For example,in a typical capacitance diaphragm pressure sensor, a thin diaphragm canmeasure down to 10⁻⁵ Torr. Thicker, but more rugged diaphragms canmeasure in the low vacuum to atmospheric range. To cover a wide vacuumrange, two or more capacitance sensing heads can be connected into amulti-range package.

Systems that utilize differential capacitance manometers generally havestringent requirements for the repeatability of pressure readings, withoffset drift typically limited to 0.02% of full scale per day. Fullscale deflection for a differential capacitance manometer typicallycauses capacitance changes of 0.2 2.0 pF (10⁻¹² F). Thus, the electronicinterface (“Analog Front End” or “AFE”) to the sensing element may notexperience drift in excess of 0.04 femtoFarad (10⁻¹⁵ F) per day.

In addition to stringent performance requirements, customers areincreasingly requiring features that allow differential capacitancemanometer based systems to take advantage of advancements in otherprocess equipment. For example, digital communications, embeddeddiagnostics and lower temperature sensitivity are now required by someof the latest process technologies. Legacy capacitance diaphragm gaugesoften cannot meet these requirements.

SUMMARY OF INVENTION

One or more of the problems outlined above may be solved by the variousembodiments of the invention. Broadly speaking, the invention comprisessystems and methods for digitally controlling sensors. The variousembodiments of the invention may substantially reduce or eliminate thedisadvantages and issues associated with prior art systems and methodsfor operating sensors.

In one embodiment, a digital controller for a capacitance diaphragmgauge is embedded in a digital signal processor (DSP). The controllerreceives digitized input from a sensor analog front end via a variablegain module, a zero offset module and an analog-to-digital converter(ADC). The controller automatically scales the received input byadjusting the variable gain and zero offset modules. The controller alsomonitors and adjusts a heater assembly to maintain an appropriatetemperature at the sensor. The controller utilizes a kernel softwaremodule that allocates processing resources to the various tasks of agauge controller module. The kernel module repetitively executesiterations of a loop, wherein in each iteration, all of a set of highpriority tasks are performed and one of a set of lower priority tasksare performed. The controller module thereby provides sensor measurementoutput at precisely periodic intervals, while performing ancillaryfunctions (e.g., automatic scaling, zero offset adjustment and embeddeddiagnostics) as well.

The present systems and methods may provide a number of advantages overthe prior art. For example, they may enable the controller tosimultaneously service the digital tool controller interface and theembedded diagnostics port interface. Further, they may enable embeddeddiagnostics within the controller. The digital engine of the controllercan discretely monitor system variables and seamlessly present the datato the tool controller and/or the embedded diagnostics port. Systemvariables may include but are not limited to the gauge pressure, sensortemperature(s), heater drive(s), ambient temperature, preprocessed gaugepressure, zero offset, and device status. Still further, there is noneed for potentiometers for manual adjustments in the present systemsand methods. Except for a single gauge balancing resistor manuallyinstalled during assembly, all calibration adjustments are madedigitally by an automated calibration stand. All calibration parametersare stored in nonvolatile memory and are accessible via the embeddeddiagnostics port. Still further, the present systems and methods mayenable linearization of the gauge and configuration of the sensor heatercontroller via the embedded diagnostics port.

BRIEF DESCRIPTION OF DRAWINGS

Other objects and advantages of the invention may become apparent uponreading the following detailed description and upon reference to theaccompanying drawings.

FIG. 1 is a hardware block diagram illustrating an embedded systemcontroller in one embodiment.

FIG. 2 is a flow chart illustrating the operation of the kernel moduleof the embedded system in one embodiment.

FIG. 3 is a block diagram illustrating the gauge controller module ofthe embedded system in one embodiment.

While the invention is subject to various modifications and alternativeforms, specific embodiments thereof are shown by way of example in thedrawings and the accompanying detailed description. It should beunderstood, however, that the drawings and detailed description are notintended to limit the invention to the particular embodiment which isdescribed. This disclosure is instead intended to cover allmodifications, equivalents and alternatives falling within the scope ofthe present invention as defined by the appended claims.

DETAILED DESCRIPTION

Overview.

A preferred embodiment of the invention is described below. It should benoted that this and any other embodiments described below are exemplaryand are intended to be illustrative of the invention rather thanlimiting.

Broadly speaking, the invention comprises systems and methods fordigitally controlling sensors. The various embodiments of the inventionmay substantially reduce or eliminate the disadvantages and issuesassociated with prior art systems and methods for operating sensors.

In one embodiment, a digital controller for a capacitance diaphragmgauge is embedded in a digital signal processor (DSP). The controllerreceives digitized input from a sensor AFE via a variable gain module, azero offset module and an analog-to-digital converter (ADC). Thecontroller automatically scales the received input by adjusting thevariable gain and zero offset modules. The controller also monitors andadjusts a heater assembly to maintain an appropriate temperature at thesensor.

The controller utilizes a kernel module that allocates processingresources to the various tasks of a gauge controller module. The kernelmodule repetitively executes iterations of a loop, wherein in eachiteration, all of a set of high priority tasks are performed and one ofa set of lower priority tasks is performed. In one embodiment, the highpriority tasks comprise reading the digitized input from the sensor,linearizing the input, and providing a pressure output. The lowerpriority tasks comprise servicing serial communication interface (SCI)messages, servicing control area network (CAN) messages, compensatingfor ambient temperature, controlling the sensor heater, controllingtemperature and status LEDs, checking for zero pressure and overpressureand the like.

The digital engine of the controller monitors system variables for thepurpose of producing accurate, repeatable, and temperature compensatedpressure output, while simultaneously supporting a digital toolcontroller interface, an independent diagnostics interface, a closedloop heater controller and other gauge functionality. All of thesefunctions are executed without affecting the accuracy or performance ofthe gauge.

Advantages. In order to meet many of the new requirements fordifferential capacitance manometer systems, a digital control system maybe required. Traditional analog signals are susceptible to noise, groundloops, and signal loss. These issues can be resolved with digitalcommunications, due to their immunity to noise and signal degradation.In one embodiment, a digital communication interface on the gauge isimplemented using an embedded digital control system.

The prior art provides few, if any, diagnostic features. Traditionalanalog gauges must be removed from the tool to be diagnosed. Using thepresent systems and methods, the gauges need not be removed in order todiagnose or resolve problems. Internal system parameters may bemonitored or retrieved during normal operation through, for example, adigital diagnostics port, or an interface to a PC, notebook computer,PDA or calibration stand. The gauges may also include embeddeddiagnostics to facilitate resolution of tool or gauge problems. Suchfeatures may reduce the cost of ownership by allowing tool or sensorissues to be quickly identified and resolved.

Conventional analog gauges are calibrated by adjusting a number ofpotentiometers through a process that is primarily one of manualcalibration. The present systems and methods, however, may provide forautomatic calibration (e.g., by an automated calibration stand). In oneembodiment, an embedded digital engine enables automated calibration andtesting, which lowers the cost of manufacturing and reduces variabilityfrom device to device. No potentiometers are required, in contrast tothe prior art. Since calibration is done digitally and automatically,there is much less chance of human induced variability. Higher levels ofaccuracy, repeatability, and device-to-device reproducibility aretherefore possible.

High performance capacitance diaphragm gauges are typically subject totemperature coefficient requirements. That is, the sensitivity of thegauges to temperature variations should be minimal. Reducing temperaturecoefficient values generally requires a precision sensor heater controlsystem. Advanced heater control is also facilitated by the presentsystems and methods, which use digital techniques to monitor and controlheater output. The present systems and methods also utilize measurementsof ambient temperature to compensate for variations in the temperatureof the electronic circuit.

The present systems and methods therefore provide high levels of gaugeperformance, while enabling simultaneous digital communications withhost equipment and diagnostics facilities. Furthermore, the presentsystems and methods may reduce the cost of manufacturing of the gaugesand the cost of ownership of the end user.

Preferred Embodiment

Referring to FIG. 1, a functional block diagram illustrating thestructure of a sensor system having a digital controller is shown. Inthe embodiment depicted in this figure, a controller is implemented in adigital signal processor (DSP) 110. In other embodiments, the controllermay be implemented in a microcontroller or other data processor. Thecontroller receives digitized input from the sensor 10, processes theinput, controls the sensor and related components, performs variousservice functions and provides output data to a user. In one embodiment,the controller DSP is embedded in (integral with) the sensor.

Pressure Acquisition. In this embodiment, a signal from the sensor(e.g., capacitance diaphragm gauge) 10 is converted to a voltage by theAnalog Front End (AFE) 30. The AFE signal is then amplified by aprogrammable gain amplifier 40 and zero adjusted by a zero offset module50. Both programmable gain amplifier 40 and zero offset module 50 arecontrolled by the embedded controller, DSP 110. The amplified and offsetanalog signal is then converted to a digital signal by analog-to-digitalconverter (ADC) 60. ADC 60 then communicates the digital signal to theprocessor upon command from the embedded control code.

Programmable gain amplifier 40 and zero offset module 50 are used tomodify the signal generated by AFE 30 because sensor outputs can varysignificantly from one sensor to another. The signal is thereforeautomatically adjusted to appropriate levels prior to digitization.These components replace the potentiometers used in prior art systemsfor gain and offset adjustments. By eliminating the potentiometers,which are susceptible to incorrect adjustment and which typically havehigh temperature coefficients, gauge performance is improved.

Signal Processing. The digitized pressure signal received by DSP 110 isprocessed using digital techniques to convert the nonlinear sensorsignal to a linear pressure signal. This process employs a linearizationalgorithm that is based on constants computed during the automaticcalibration of the controller. These constants are maintained innon-volatile memory in the EEPROM 150. A temperature compensationalgorithm is also used to process the signal to compensate fortemperature variations in the electronics.

After the digital signal is processed by the DSP, it can be sent to oneor more output ports. The digital signal can be transmitted directly toa digital device or network, such as control area network (CAN)transceiver 101, which can then make it available to a DeviceNet network102, or an RS232/485 embedded diagnostics port, through which it can bemade available to a calibration stand, PC, or other devices. Theprocessed digital signal may also be sent to a digital-to-analogconverter (DAC) 70 to produce an analog signal suitable for an analogThe analog signal may be scaled by circuit 103 and linearized by analgorithm if necessary prior to being conveyed to the device 104.

Zero Offset. The zero offset is the output of the gauge when it isexposed to a base pressure or a pressure which is below the detectionresolution of the gauge. One of the problems with conventional CDGs iscontrol of zero offset drift in the gauge. Most gauges will experiencesome drift or shifting of the zero offset value over time. The gaugestherefore need to be periodically adjusted to compensate for the drift.Conventional gauges require that a user (e.g., a technician) adjust apotentiometer until the gauge output shows zero volts when it is exposedto base pressure.

The present systems and methods simplify this zero adjust procedure byeliminating the adjustment potentiometer. The controller is configuredto monitor the pressure signal and automatically adjust zero offsetmodule 50 in response to an appropriate command. Because the adjustmentof the zero offset is automatically performed by the controller, thetime required to adjust the zero offset is minimized. There is also areduced risk of incorrect adjustment because the opportunity for humanerror in adjustment of a potentiometer is eliminated. (It should also benoted that the accuracy of the adjustment is typically substantiallygreater than can be obtained by manual adjustment of a potentiometer.)The zero adjust procedure may be invoked manually (e.g., by a userpressing a button) or it may be initiated in response to a signal fromthe tool port, the diagnostics port, contact closure, or even thecontroller itself.

In one embodiment, the controller incorporates a lock out featurerelating to the zero adjust procedure. Adjustment of the zero offsetshould only be performed when the appropriate conditions exist. If oneof these conditions is not met, error may be introduced into thesubsequent measurements. In one embodiment, the following conditionsshould be met before a zero adjust procedure is performed: the inletpressure should be below the zero adjust limit of the gauge; the sensorshould be at the set point temperature; the ambient temperature of theelectronics should be within a predetermined range; an overpressuresignal should not be asserted; and no fault conditions should existwithin the sensor or controller. Because failure to observe theseconditions may result in improper adjustment, the controller isconfigured to prevent the zero adjustment from taking place unless theseconditions are met.

Variable gain. The controller may also provide for automatic calibrationof the system. Because the sensor signal may not have the optimal signalrange (i.e., magnitude and displacement from zero), it is at timesnecessary to adjust the variable gain module, as well as the zero offsetmodule, to obtain the best possible signal to input to theanalog-to-digital converter and controller. The controller is configuredto provide control inputs to the variable gain and zero offset modulesand thereby adjust them. This eliminates the need to manually adjustpotentiometers as in conventional systems. By adjusting these modulesbased on the digitized sensor signal, the accuracy and repeatability ofthe calibration is improved.

Heater Control. In this embodiment, the controller is also responsiblefor controlling the sensor heater assembly 20. The heater assembly isnecessary in this embodiment because the sensor output is a function oftemperature, and because sensor performance may be affected by thecondensation of process gasses on the diaphragm of the sensor (acapacitance diaphragm gauge). The controller therefore monitors thetemperature of the sensor and adjusts the temperature of the heaterassembly to maintain the desired set point temperature at the sensor.The control of the heater is implemented in a closed loop subsystemwhich is operated in parallel with other system functions and which doesnot degrade gauge accuracy or performance.

Ambient Temperature Compensation. Ambient temperature also has an effecton the performance of the sensor, although it is generally less than theeffect of sensor temperature. The controller is therefore coupled to anambient temperature sensor 140. The controller receives ambienttemperature information from sensor 140 and processes the digital signalto compensate for the effects of ambient temperature.

Digital Communications Ports. As noted above, the controller can providethe processed digital signal to a number of ports for use by variousother devices. For instance, the controller may have a CAN interface forsending data to CAN transceiver 101, which can then send the data to aDeviceNet network. The controller likewise has a pressure output portcoupled to DAC 70, which can provide an analog signal (corresponding tothe digital signal) to external analog devices. Still further, thecontroller can send the data via a PART (universal asynchronousreceiver/transmitter) to an RS232/485 diagnostics port 100. Diagnosticsport 100 is independent and is available to enable automaticcalibration, testing, and troubleshooting features of the controller.This port enables the controller to provide diagnostic data via a seriallink to a PC, laptop, PDA, calibration stand or the like (105). Thediagnostics port may also enable remote diagnostics if it is interfacedwith an appropriate web server device.

Other Hardware Modules. Other signals monitored by the controller inthis embodiment include the address, baud rate selector and MacIDswitches (160), and various status (e.g., fault) and temperature LEDs(170). The status and temperature LEDs may be driven by embeddeddiagnostics in the controller. The controller also interfaces with anon-volatile memory (e.g., EEPROM 150) to store calibration andconfiguration parameters. These hardware features are discussed in moredetail elsewhere in this disclosure.

Software. The DSP in which the controller is implemented is programmedto periodically execute certain tasks, including the functional tasksinvolved in processing sensor signals and the ancillary tasks involvedin the diagnostic, calibration and other non-measurement functions. Thisprogramming is implemented in one embodiment by a kernel module and acontroller module. The kernel module executes continually and allocatesprocessing resources to the various tasks that are to be performed,while the controller module actually performs the tasks.

Kernel Module. As noted above, the kernel in this embodiment of theembedded controller allocates processor resources to the individualtasks of the controller module. Because the primary purpose of theembedded controller is to control a sensor, the first priority of thecontroller is to service the sensing functions of the system. The kernelis designed to provide precisely periodic service of these functions. Inthis embodiment, these functions include reading the digitized pressuresignal from the analog-to-digital converter, linearizing the digitizedpressure signal and providing the linearized signal to the variousoutput ports (particularly those intended specifically for sensoroutput). By allocating resources to these high priority tasks first, thekernel ensures timely and accurate determination of the sensed pressure.

Since the embedded controller in this embodiment is used in a closedloop pressure control system, it is important that the controller doesnot induce any variations in its pressure response time. If thefunctions relating to the processing of the pressure signal weredelayed, the pressure control system would effectively be operating withstale data and would produce potentially erroneous control data. Thekernel therefore allocates processor resources to the lower prioritytasks in such a way as not to delay or interrupt the high prioritypressure calculation tasks.

The kernel is paced by a timer which periodically generates interruptsthat trigger the high priority pressure calculation tasks. Eachinterrupt triggers a new iteration of a control flow that includesexecution of all of the high priority tasks and, in this embodiment, oneof the lower priority tasks. Each high priority task completes executionprior to the next timer interrupt. The remainder of the time before thenext interrupt can be used for the lower priority tasks.

In one embodiment, the high priority tasks include: reading the AFEoutput from the analog-to-digital converter; calculating the linearizedpressure output; writing the linearized pressure value to the DAC(s);servicing CAN buffers; and servicing serial port buffers.

The lower priority tasks in this embodiment include: processing serialcommunication messages (via embedded diagnostics port 100); processingCAN messages (via DeviceNet port 101); updating ambient temperaturecompensation; servicing closed loop heater algorithm; servicingtemperature LEDs; monitoring overpressure and zero adjust inputs;servicing status LEDs 170 and switches 160; and servicing EEPROM 150.

Referring to FIG. 2, a flow diagram illustrating the operation of theembedded system kernel is shown. Upon power-up (or a reset event), thekernel allocates resources to the initialization of the DSP, includingthe controller module and the kernel module itself. After initializationis complete, the kernel repetitively executes loop 200, which consistsgenerally of steps 220 and 230. Each iteration of this loop is executedin response to a signal from timer 210, ensuring that the loop isexecuted in a precisely periodic manner.

Step 220 comprises the tasks that are involved in the processing ofsensor output to generate an output signal (i.e., the high prioritytasks). In the embodiment described above, these tasks comprise readingthe digital signal produced by analog to digital converter 60,linearizing this signal to produce a linear pressure output signal,performing temperature compensation adjustment of the pressure signaland writing the resulting pressure data to the buffers out of thedigital to analog converter, CAN and diagnostic (SCI) ports. Each ofthese tasks is executed once in every iteration of the loop. Themeasurement function of the sensor controller system therefore has thesame periodicity as timer 210.

After the high priority tasks of step 220 are performed, one of thelower priority tasks is selected in step 230. Each of these tasks isshown in the figure as a separate step (240-247). In the embodimentdepicted in the figure, the lower priority tasks comprise: servicing SCImessages (240); servicing CAN messages (241); performing temperaturecompensation (242); performing heater control (243); controllingtemperature LEDs (244); performing zero and overpressure checks (245);controlling status LEDs (246); and controlling EEPROM and elapsed-timetimers (247). The lower priority task to be executed in a giveniteration of the loop is selected based upon a task counter that isincremented upon completion of the lower priority task in each loop (seestep 250). Consequently, the lower priority tasks of steps 240-247 areexecuted sequentially, one per iteration of loop 200. Put another way,each low priority task is serviced every “N” timer iterations, where “N”is the number of tasks in the task list.

In this embodiment, the timer 210 that controls the initiation of eachiteration of loop 200 is a set to allow sufficient time for completionof all of the high priority tasks and any one of the lower prioritytasks (as well as the incrementing of the task counter). In otherembodiments, it may be desirable to shorten the timer cycle to providemore frequent updates of the sensor output reading generated by thecontroller. In this instance, there may not be sufficient time tocomplete the selected lower priority task. Provisions may therefore bemade in the design to allow for incomplete execution of a selected taskand resumption or re-execution of the task at a later time.Alternatively, it may not be necessary to frequently update the sensoroutput reading of the controller. In this instance, it may be possibleto increase the interval of the timer so that more than one of the lowerpriority tasks can be completed in a single iteration of the loop. Othervariations may also be possible.

Using the kernel control loop shown in FIG. 2, each task completesbefore the next timer interrupt occurs. This sequential process ensuresthat the gauge control system is able read, linearize, and outputchamber pressure in a precisely periodic manner while also servicing allother gauge functions. This control flow effectively prioritizescomputational resources for the purpose of maximizing gauge accuracy andperformance, while still ancillary functions.

Controller Module. As mentioned above, the controller module executesthe tasks of the embedded controller as resources are allocated by thekernel. The structure of the controller module is shown in FIG. 3. Thestructure is described below with reference to the figure.

In one embodiment, the controller module software is programmed into aDSP. (It should be noted that “software” as used here refers to a set ofprogram instructions configured to cause the DSP to perform a designatedtask, and is intended to include software, firmware and hard-codedinstructions.) The controller module is configured to receive data fromthe heater assembly and sensor, the AFE and the analog-to-digitalconverter. The controller module also receives control input from thezero button (when a user pushes the button to initiate the automaticre-zeroing process). The controller module provides output data in thisembodiment to the CAN port, the digital-to-analog converter and thediagnostics port (RS232/485). The controller module provides controloutput to the analog zero offset and gain components, as well as theheater assembly and sensor.

Controller module 300 includes a heater controller module 310 that isconfigured to receive temperature data from temperature sensors coupledto sensor 10. Heater controller module 310 processes this data todetermine whether the temperature of sensor 10 is appropriate and toadjust the temperature if necessary. This may involve separatelycontrolling multiple heating components corresponding to different zonesof sensor 10. Heater set point and tuning values are stored in theEEPROM and are restored on power-up.

Zero adjust module 330 is configured to initiate the zero offsetadjustment procedure in response to a signal received from the zerobutton. Zero adjust module 330 automatically determines the drift of thesensor and/or analog front end so that it can be corrected. In otherwords, zero adjust module 330 determines the adjustment necessary tocause the sensor signal digitized by the analog-to-digital converter tobe zero when the pressure is effectively zero (i.e., below a minimumresolvable pressure.) This information can then be sent to a zero offsetcontrol module, which in turn causes the actual adjustment of the zerooffset hardware module. The adjustment is stored in the EEPROM and isrestored on power up.

It should be noted that, in one embodiment, zero adjust module 330incorporates a lock out feature. This prevents zero offset adjustment ifthe appropriate conditions for the adjustment (those for which theadjustment can be properly executed) are not met. In other words, theautomatic zero offset adjustment procedure is locked out. The specificconditions that must be met in this embodiment are that the pressure atthe sensor is below a predetermined threshold, the sensor temperature isat the desired setpoint, the ambient temperature of the electronics iswithin a predetermined range, and no fault conditions are present in thecontroller.

EEPROM module 320 is configured to manage the storage of data in theEEPROM (electronically erasable programmable read only memory). TheEEPROM module stores gain and zero adjust values, configuration data,historical diagnostic data, and heater configuration and control data.As noted above, the linearization constants that are computed bycontroller module 300 are also stored in the EEPROM. These constants areused by pressure linearization module 340 to convert the non-lineardigitized signal received from the analog-to-digital converter into alinear pressure signal that can be output through the appropriate ports.It should be noted that the linear pressure signal produced by pressurelinearization module 340 may have to be processed by temperaturecompensation module 350 in order to correct for changes in ambienttemperature.

Once the pressure signal is linearized and temperature compensated, itcan be sent to the appropriate output modules. In one embodiment, thesemodules include a tool controller module 360 that is configured tocontrol output to a CAN port (which may be made available a DeviceNetnetwork), an embedded diagnostics and calibration module 370 that isconfigured to control output to the dedicated diagnostics port, and adigital-to-analog converter module 380 that is configured to controloutput to the digital-to-analog converter.

Embedded diagnostics and calibration module 370 enables communicationbetween the controller module and an external device such as acalibration stand or a PC. The controller can therefore performdiagnostic procedures using the digital signal data and internalcontroller data and then communicate this information to a user. Itshould be noted that the particular diagnostics performed may vary fromone embodiment to another, so no specific procedures will be discussedhere. The programming of particular procedures is believed to be withinthe abilities of a person of ordinary skill in the art of the invention.The diagnostics may produce indications of fault conditions, which mayin turn be communicated to a user, used to drive LED indicators, usedfor other diagnostic procedures and so on. In one embodiment, the faultconditions are recorded in a historical database for later analysis.

The calibration performed by embedded diagnostics and calibration module370 also utilizes communications from an external device, i.e., acalibration stand. The module is configured to receive data downloadedfrom the calibration stand, such as calibration constants or other datadescribing the multivariable response function utilized in thecalibration procedures. This information can then be used, along withinternal variables such as the unprocessed sensor signal, the ambienttemperature, sensor temperature and the overpressure signal, to adjustthe variable gain and zero offset hardware modules to obtain optimizedinput data.

It can be seen from FIG. 3 that, in addition to the zero offset controlmodule which controls the offset of the analog sensor signal, controllermodule 300 includes a sensor gain control module. This module controlsthe programmable gain hardware module that amplifies the analog sensorsignal from the analog front end. This allows the most appropriatesignal level to be provided to the input of the analog-to-digitalconverter. Both the amplifier gain and zero adjust values are stored inEEPROM and are restored at power up. Controller module 300 additionallyincludes an overpressure input module that is configured to sense anoverpressure condition in the analog front end.

In addition to the embodiments of the invention described above, thereare various alternative embodiments that are within the scope of thepresent disclosure. For example, one alternative embodiment may comprisea sensor system having a sensor, an analog front end, ananalog-to-digital converter and a digital controller, as describedabove. This system may include other hardware components, alone or incombination. These components may include a sensor heater, a variablegain module, a zero offset module, a memory (e.g., an EEPROM),communication ports, calibration stands, PCs, PDAs, networks, or otherexternal equipment.

Other embodiments may comprise methods. For example, one alternativeembodiment comprises a method for performing a zero adjustment. Thismethod includes the following steps: detecting a zero adjust command(e.g., from a user pushbutton switch, a contact closure, or a digitalcommand from a communication ports); sensing the zero offset value ofthe inlet pressure signal; digitally removing the zero offset signalfrom the linearized pressure output signal; and updating the zero adjuststatus variable. This method may further include the steps of indicatingthe success or failure of the zero adjust operation, performing theprocedure only if predetermined conditions are met (otherwise lockingout the procedure), and so on.

Yet another alternative embodiment may comprise a method for calibratinga sensor such as a capacitance diaphragm gauge. The steps of this methodmay comprise: measuring the actual pressure at the sensor inlet; sensinga series of system variables associated with the capacitance diaphragmgauge (e.g., unprocessed input pressure signal, ambient temperaturesignal, sensor temperature signals or overpressure signal); controllinganother series of system variables associated with the capacitancediaphragm gauge (e.g., sensor gain amplifier value or zero offsetvalue); modeling the pressure with a regression technique to produce amultivariable response function describing the gauge pressure in termsof the system variables; and inputting the multivariable responsefunction into an embedded control system to enable the output of apressure signal.

The benefits and advantages which may be provided by the presentinvention have been described above with regard to specific embodiments.These benefits and advantages, and any elements or limitations that maycause them to occur or to become more pronounced are not to be construedas a critical, required, or essential features of any or all of theclaims. As used herein, the terms “comprises,” “comprising,” or anyother variations thereof, are intended to be interpreted asnon-exclusively including the elements or limitations which follow thoseterms. Accordingly, a process, method, article, or apparatus thatcomprises a list of elements does include only those elements but mayinclude other elements not expressly listed or inherent to the claimedprocess, method, article, or apparatus.

While the present invention has been described with reference toparticular embodiments, it should be understood that the embodiments areillustrative and that the scope of the invention is not limited to theseembodiments. Many variations, modifications, additions and improvementsto the embodiments described above are possible. It is contemplated thatthese variations, modifications, additions and improvements fall withinthe scope of the invention as detailed within the following claims.

1. A pressure sensing system comprising: a pressure sensor; an analogfront end module, coupled to the pressure sensor, to produce an analogpressure sensor signal; an analog-to-digital converter to convert theanalog pressure sensor signal to a digital sensor signal; and a digitalcontroller configured to receive the digital sensor signal, linearizethe digital sensor signal, and provide an output signal that is basedupon the linearized digital sensor signal during each iteration of acontrol loop executed by the digital controller in which the digitalcontroller performs at least one additional task.
 2. The pressuresensing system of claim 1, wherein the digital controller is configuredto provide the output signal that is based upon the linearized digitalsensor signal by at least one of writing the output signal to adigital-to-analog converter and writing the output signal to one or moreport buffers.
 3. The pressure sensing system of claim 2, wherein the atleast one additional task includes at least one or more of: processingcommunication messages received from a diagnostics port; processingcontrol area network messages; performing ambient temperaturecompensation; performing a closed loop heater algorithm; servicingtemperature LEDs; monitoring overpressure and zero adjust inputs;servicing status LEDs and switches; servicing an EEPROM; performing anautomatic analog scaling procedure; performing an automatic zero adjustprocedure; and performing an embedded diagnostic procedure.
 4. Thepressure sensing system of claim 3, further comprising: a variable gainmodule, coupled between the analog front end module and theanalog-to-digital converter, to adjust a gain of the analog pressuresensor signal prior to digitization by the analog-to-digital converter.5. The pressure sensing system of claim 4, further comprising: a zerooffset module, coupled between the variable gain module and theanalog-to-digital converter, to adjust a zero offset of the analogpressure sensor signal prior to digitization by the analog-to-digitalconverter.
 6. The pressure sensing system of claim 5, wherein thevariable gain module and the zero offset module each receives arespective digital control signal from the digital controller torespectively adjust the gain and the zero offset of the analog pressuresensor signal.
 7. The pressure sensing system of claim 1, wherein the atleast one additional task includes at least one or more of: processingcommunication messages received from a diagnostics port; processingcontrol area network messages; performing ambient temperaturecompensation; performing a closed loop heater algorithm; servicingtemperature LEDs; monitoring overpressure and zero adjust inputs;servicing status LEDs and switches; servicing an EEPROM; performing anautomatic analog scaling procedure; performing an automatic zero adjustprocedure; and performing an embedded diagnostic procedure.
 8. Thepressure sensing system of claim 1, further comprising: a variable gainmodule, coupled between the analog front end module and theanalog-to-digital converter, to adjust a gain of the analog pressuresensor signal prior to digitization by the analog-to-digital converter.9. The pressure sensing system of claim 8, wherein the variable gainmodule receives a digital control signal from the digital controller toadjust the gain of the analog pressure sensor signal.
 10. The pressuresensing system of claim 8, further comprising: a zero offset module,coupled between the variable gain module and the analog-to-digitalconverter, to adjust a zero offset of the analog pressure sensor signalprior to digitization by the analog-to-digital converter.
 11. Thepressure sensing system of claim 1, further comprising: a zero offsetmodule, coupled between the analog front end module and theanalog-to-digital converter, to adjust a zero offset of the analogpressure sensor signal prior to digitization by the analog-to-digitalconverter.
 12. The pressure sensing system of claim 11, wherein the zerooffset module receives a digital control signal from the digitalcontroller to adjust the zero offset of the analog pressure sensorsignal.
 13. A method for controlling a pressure sensing systemcomprising acts of: receiving an analog pressure sensor signal;converting the analog pressure sensor signal to a digital sensor signal;reading the digital sensor signal; linearizing the digital sensorsignal; providing an output signal based upon the linearized digitalsensor signal; and performing at least one additional task; wherein theacts of reading, linearizing, and providing are performed by a digitalcontroller during each iteration of a control loop executed by thedigital controller in which the digital controller performs the at leastone additional task.
 14. The method of claim 13, wherein the act ofproviding the output signal includes at least one of writing thelinearized digital sensor signal to a digital-to-analog converter andconveying the linearized digital sensor signal to one or more portbuffers.
 15. The method of claim 14, wherein the at least one additionaltask includes at least one or more of: processing communication messagesreceived from a diagnostics port; processing control area networkmessages; performing ambient temperature compensation; performing aclosed loop heater algorithm; servicing temperature LEDs; monitoringoverpressure and zero adjust inputs; servicing status LEDs and switches;servicing an EEPROM; performing an automatic analog scaling procedure;performing an automatic zero adjust procedure; and performing anembedded diagnostic procedure.
 16. The method of claim 15, furthercomprising an act of: digitally adjusting a gain of the analog pressuresensor signal prior to the act of converting the analog pressure sensorsignal to a digital sensor signal.
 17. The method of claim 16, furthercomprising an act of: digitally adjusting a zero offset of the analogpressure sensor signal prior to the act of converting the analogpressure sensor signal to a digital sensor signal.
 18. The method ofclaim 17, wherein the act of digitally adjusting the gain is performedprior to the act of digitally adjusting the zero offset.
 19. The methodof claim 13, further comprising an act of: digitally adjusting a gain ofthe analog pressure sensor signal prior to the act of converting theanalog pressure sensor signal to a digital sensor signal.
 20. The methodof claim 13, further comprising an act of: digitally adjusting a zerooffset of the analog pressure sensor signal prior to the act ofconverting the analog pressure sensor signal to a digital sensor signal.